The usage of ISBSG data fields in software effort estimation: A systematic mapping study

[EN] The International Software Benchmarking Standards Group (ISBSG) maintains a repository of data about completed software projects. A common use of the ISBSG dataset is to investigate models to estimate a software project's size, effort, duration, and cost. The aim of this paper is to determine which and to what extent variables in the ISBSG dataset have been used in software engineering to build effort estimation models. For that purpose a systematic mapping study was applied to 107 research papers, obtained after a filtering process, that were published from 2000 until the end of 2013, and which listed the independent variables used in the effort estimation models. The usage of ISBSG variables for filtering, as dependent variables, and as independent variables is described. The 20 variables (out of 71) mostly used as independent variables for effort estimation are identified and analysed in detail, with reference to the papers and types of estimation methods that used them. We propose guidelines that can help researchers make informed decisions about which ISBSG variables to select for their effort estimation models.González-Ladrón-De-Guevara, F.; Fernández-Diego, M.; Lokan, C. (2016). The usage of ISBSG data fields in software effort estimation: A systematic mapping study. Journal of Systems and Software. 113:188-215. doi:10.1016/j.jss.2015.11.040S18821511

Explanatory and Causality Analysis in Software Engineering

Software fault proneness and software development efforts are two key areas of software engineering. Improving them will significantly reduce the cost and promote good planning and practice in developing and managing software projects. Traditionally, studies of software fault proneness and software development efforts were focused on analysis and prediction, which can help to answer questions like `when’ and `where’. The focus of this dissertation is on explanatory and causality studies that address questions like `why’ and `how’. First, we applied a case-control study to explain software fault proneness. We found that Bugfixes (Prerelease bugs), Developers, Code Churn, and Age of a file are the main contributors to the Postrelease bugs in some of the open-source projects. In terms of the interactions, we found that Bugfixes and Developers reduced the risk of post release software faults. The explanatory models were tested for prediction and their performance was either comparable or better than the top-performing classifiers used in related studies. Our results indicate that software project practitioners should pay more attention to the prerelease bug fixing process and the number of Developers assigned, as well as their interaction. Also, they need to pay more attention to the new files (less than one year old) which contributed significantly more to Postrelease bugs more than old files. Second, we built a model that explains and predicts multiple levels of software development effort and measured the effects of several metrics and their interactions using categorical regression models. The final models for the three data sets used were statistically fit, and performance was comparable to related studies. We found that project size, duration, the existence of any type of faults, the use of first- or second generation of programming languages, and team size significantly increased the software development effort. On the other side, the interactions between duration and defective project, and between duration and team size reduced the software development effort. These results suggest that software practitioners should pay extra attention to the time of the project and the team size assigned for every task because when they increased from a low to a higher level, they significantly increased the software development effort. Third, a structural equation modeling method was applied for causality analysis of software fault proneness. The method combined statistical and regression analysis to find the direct and indirect causes for software faults using partial least square path modeling method. We found direct and indirect paths from measurement models that led to software postrelease bugs. Specifically, the highest direct effect came from the change request, while changing the code had a minor impact on software faults. The highest impact of the code change resulted from the change requests (either for bug fixing or refactoring). Interestingly, the indirect impact from code characteristics to software fault proneness was higher than the direct impact. We found a similar level of direct and indirect impact from code characteristics to code change

Handling Categorical Variables in Effort Estimation

Background: Accurate effort estimation is the basis of the software development project management. The linear regression model is one of the widely-used methods for the purpose. A dataset used to build a model often includes categorical variables denoting such as programming languages. Categorical variables are usually handled with two methods: the stratification and dummy variables. Those methods have a positive effect on accuracy but have shortcomings. The other handing method, the interaction and the hierarchical linear model (HLM), might be able to compensate for them. However, the two methods have not been examined in the research area. Aim: giving useful suggestions for handling categorical variables with the stratification, transforming dummy variables, the interaction, or HLM, when building an estimation model. Method: We built estimation models with the four handling methods on ISBSG, NASA, and Desharnais datasets, and compared accuracy of the methods with each other. Results: The most effective method was different for datasets, and the difference was statistically significant on both mean balanced relative error (MBRE) and mean magnitude of relative error (MMRE). The interaction and HLM were effective in a certain case. Conclusions: The stratification and transforming dummy variables should be tried at least, for obtaining an accurate model. In addition, we suggest that the application of the interaction and HLM should be considered when building the estimation model

Handling categorical variables in effort estimation

Background: Accurate effort estimation is the basis of the software development project management. The linear regression model is one of the widely-used methods for the purpose. A dataset used to build a model often includes categorical variables denoting such as programming languages. Categorical variables are usually handled with two methods: the stratification and dummy variables. Those methods have a positive effect on accuracy but have shortcomings. The other handing method, the interaction and the hierarchical linear model (HLM), might be able to compensate for them. However, the two methods have not been examined in the research area. Aim: giving useful suggestions for handling categorical variables with the stratification, transforming dummy variables, the interaction, or HLM, when building an estimation model. Method: We built estimation models with the four handling methods on ISBSG, NASA, and Desharnais datasets, and compared accuracy of the methods with each other. Results: The most effective method was different for datasets, and the difference was statistically significant on both mean balanced relative error (MBRE) and mean magnitude of relative error (MMRE). The interaction and HLM were effective in a certain case. Conclusions: The stratification and transforming dummy variables should be tried at least, for obtaining an accurate model. In addition, we suggest that the application of the interaction and HLM should be considered when building the estimation model